1. Field of the Invention
The present invention relates to a piston ring assembly for a Stirling engine and particularly, to an improved piston ring assembly for use in a Stirling engine so as to reduce the number of parts thereof so that the piston ring assembly is simple in construction, inexpensive to manufacture, durable in use, and easy in assembly.
2. Description of the Prior Art
Generally, various types of piston rings for use in a Stirling engine mounted on an external circumferential surface of a piston and inserted into the interior of a cylinder are well known in the art. Such piston rings are closely connected to the internal peripheral surface of the cylinder for preventing operational gas from leaking into the interior of the cylinder through a gap between the piston and the cylinder. And since such piston rings for use in the Stirling engine have to execute a tight sealing operation for a non-lubricating state, such piston rings are made of teflon resin for executing the sealing operation and self-lubricating operation without using a cast iron ring.
One of such conventional piston rings for use in a Stirling engine is illustrated in FIGS. 1 to 4. As shown in FIGS. 1 to 4, the piston ring includes one pair of main rings 6 and 7. The main rings 6 and 7 are provided with an inner ring 8 for preventing the rotation of the main rings 6 and 7 and a tensional ring 9 for giving a tensional force to the inner ring 8 to engage with a ring groove 1a formed at the external circumferential surface of a piston 1 so as to tightly close the main rings 6 and 7 the interior surface of a cylinder 5.
Moreover, slits 6a, 7a, 8a,and 9a are formed at the main rings 6 and 7, the inner ring 8, and the tensional ring 9, respectively. The main rings 6 and 7 are engaged with the ring groove 1a of the piston 1 in which two rings 6 and 7 are necessarily superposed in order to prevent the operational gas from leaking through the slits 6a and 7a. Also, the operational gas leaks out when the main rings 6 and 7 are rotated around. Therefore, the slits 6a and 7a thereof are oppositely positioned. A pair of protrusions 8b are formed at the external circumferential surface of the inner ring 8 for being adapted to engage with the slits 6a and 7a of the main rings 6 and 7 so as to lock the slits in opposite side of one another and to prevent the main rings 6 and 7 from rotating around by themselves.
Furthermore, the tensional ring 9 gives a tensional force to the main rings 6 and 7 so that the main rings 6 and 7 are rendered to contact the internal peripheral surface of the cylinder 5 closely.
However, since the conventional piston ring structure as aforementioned is comprised of four kinds of parts such as two main rings, an inner ring, and a tensional ring, they have a number of disadvantages in that many parts are required and are complicated in construction, expensive to manufacture, and inconvenient for use.